Analog amplifiers and pre-amplifiers are often used in electronic devices to apply a multiplicative gain to a signal, in order to better condition such signal for processing by subsequent elements of a signal path. For example, pre-amplifiers may be used as part of an analog front end of a signal path in an audio system (e.g., a digital microphone system). An example of such an amplifier is the source-follower amplifier 100 shown in FIG. 1. The amplifier 100 may include an n-type field-effect transistor 102 coupled at its drain to a voltage supply, and coupled at its source to a resistor 104, which is in turn coupled to an electrical ground. In operation, amplifier 100 may receive a signal IN at a gate terminal of transistor 102 and output an output signal OUT at the source terminal of transistor 102 which is an amplified version of input signal IN.
It has been observed in transistors that during normal amplifier operation, an effect known as “charge trapping” may occur, which may alter the threshold voltage of a transistor, adding flicker noise to the output of the system. Flicker noise is a type of electronic noise with a 1/f power density spectrum over a frequency f, and is also sometimes referred to as 1/f noise. This noise is undesirable, especially in precision amplifier systems.